Propene 2,3-dibromo

To a solution of hexamethyldisilane (2.5 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) (3 ml) at 0-5 °C was added methyl lithium (2.5 mmol, 1.5 m MeLi.LiBr complex in ether) dropwise. After being stirred for 3 min, the red solution was treated with Cul (2.5 mmol) in Me2S (1 ml), the resulting black reaction mixture was stirred for 3 min. and 2,3-dibromo-propene (1 mmol) was added rapidly via a syringe. The reaction mixture was allowed to warm to room temperature, and was stirred for 1.5 h. It was then poured into pentane (25 ml) and saturated ammonium chloride solution (25 ml, buffered to pH 8 by the addition of ammonium hydroxide), and the mixture was stirred vigorously for 1 h. The aqueous phase was re-extracted with pentane, and the combined organic extracts were dried. Removal of... 

Various alkyl- and aryl-substituted [3]radialenes could be prepared from 1,1-dihaloal-kenes using organometallic pathways. Hexamethyl-[3]radialene (25), the first [3]radialene to be synthesized, was obtained in a very low yield by treatment of l,l-dibromo-2-methyl-1-propene (22) with butyllithium8,9. The lithium carbenoid 23 and the butatriene 24 are likely intermediates of this transformation (Scheme 2), the former being the source of an unsaturated carbene moiety which is transferred onto the latter. However, the outer double bonds of 24 are more readily cyclopropanated than the central one. 

However, in a non-polar solvent such as CS2 only 2,3-dibromo-l-phenyl-l-propene was formed. A control experiment indicated that at -70 °C 2,3-dibromo-3-phenyl-l-propene was also formed, which would isomerize to 2,3-dibromo-l-phenyl-l-pro-pene 19 at higher temperatures [16]. 

A. 1,1-Dibromo-2,2-bis(chloromethyl)cyclopropane (1). Into a 1-L, threenecked, round-bottomed flask, equipped with an efficient mechanical stirrer, a thermometer, and a condenser equipped with a potassium hydroxide drying tube, are placed 54.1 g (0.403 mol) of 3-chloro-2-(chloromethyl)propene (Note 1), 212 g (0.805 mol) of bromoform (Note 2), 1.70-2.00 g (14.4-16.9 mmol) of pinacol (Note 3), and 1.45 g (3.94 mmol) of dibenzo-18-crown-6 (Note 4). With very vigorous stirring (Note 5), 312 g of an aqueous 50% sodium hydroxide solution that has been cooled to 15°C is added in one portion. The reaction mixture turns orange, then brown, then black within 5 min, and the temperature of the reaction mixture begins to rise. Within 20 min, the internal reaction temperature is 49-50°C at which point the reaction flask is cooled with a room-temperature water bath, and the reaction temperature decreases to ca. 

Dibromo-1-(phenylsulfonyl)-1-propene as a Versatile Reagent for the Synthesis of Furans and Cyclopentenones. 

The formation of cyclopropane by reduction of 1,3-dibromopropane was discovered in 1887. Dissolving metals, in particular zinc dust in ethanol, were employed as an electron source [88], Electrochemical reduction in dimethyl-formamide at a mercury cathode has been found to give good yields of cyclopropane [89, 90], 1,3-dibromo, 1,3-diiodo and l-chloro-3-iodopropane all give greater than 90 % yield of cyclopropane, the other product being propene. 

Palladium-catalyzed approaches have been described and studied for the oxygenated series. Thus, treatment of 2,3-dibromo-l-propene 182 with the monoanion of catechol 181, generated with NaH, in the presence of Pd(PPh3)4 and anhydrous potassium carbonate, afforded 2,3-dihydro-2-methylene-l,4-benzodioxin 183 in 67% yield (Equation 31) <1998JA9283>. 

Dibromo-2,2-bis(chloromethyl)cyclopropane was purchased from the Aldrich Chemical Company, Inc. It can be synthesized from 3-chloro-2-chloromethyl-1-propene, available from the Aldrich Chemical Company, Inc., by phase-transfer dibromocyclopropanation.3 5.6... 

Kende, A., J. Am. Chem. Soc. 85, 1882 (1963). Since the pKa determinations of fuchsone and 2,6-dibromo-8,9-diphenylquinocyclo-propene were of necessity carried out in a nonaqueous solvent, the value for the hypothetical "aqueous pKa could easily differ 0.5 pK units from that given in Table II. 

Dibromo-l-(phenylsulfonyl)-l-propene (15) undergoes a similar addition/elimination reaction with anions of 1,3-dicarbonyl compounds (14) (Scheme 3). The addition/elimination product after decarboxylation (16) under-... 

If 2,3-dibromo propene is used as an allylic substrate the substitution product 71 can be either isolated or, after addition of additives and adjustment of the reaction conditions, 71 can readily react in cross-coupling reactions with alkynes (Sonogashira coupling), stannanes (Stille coupling), or boronic acids and boronates (Suzuki coupling) to provide the sequential allylic substitution-cross-coupling products 72-78 in moderate to good yields (Scheme 23). 

Equally, a 1.5 1 mixture of cis- and frans- 1,3-dibromo propene reacts with sodium dimethyl methylmalonate to furnish the vinyl bromo derivative 79 in excellent yield, which in turn is transformed in a one-pot fashion to a 1.5 1 mixture of enyne 80 or the corresponding Suzuki products 81 and 82 (Scheme 24). Interestingly, (( )-3-bromo-propenyl)-tributylstannane furnishes the vinyl stannane 83 upon allylic substitution that instantaneously is subjected to the conditions of a Stille coupling with iodo benzene to give the sequence s product 84 in 68% yield (Scheme 25). 

B. 2,3-Dibromo-1-(phenylsulfonyl)-1-propene. To a solution containing 25.4 g (0.14 mol) of 1-(phenylsulfonyl)-1,2-propadiene in 100 mL of acetic acid in a 250-mL, round-bottomed flask fitted with a dropping funnel is added 8.0 mL (0.14 mol) of bromine over a period of 30 min. The solution is stirred at room temperature for 8 hr, poured into 200 mL of water, and extracted with dichloromethane (3 x 100 mL). The dichloromethane layer is washed with 50 mL of a 1.0 M aqueous sodium ihiosulfate... 

D. 2-Methyl-3-[(phenylsulfonyl)methyll-2-cyclopenten-1 -one. In aflame-dried, 1-L, round-bottomed flask equipped with an addition funnel under a nitrogen atmosphere are placed 20.0 g (58.8 mmol) of 2,3-dibromo-1-(phenylsulfonyl)-1-propene and 7.0 mL (60.0 mmol) of 3-methyl-2,4-pentanedione in 300 mL of methanol (Note 8). The flask is cooled using an ice-water bath. To this mixture is added 140 mL... 

Zirconacyclopentadienes 23 (R = R = R = R = Et, Pr", Bu", M = Zr, Cp =Cp) react with l,4-dibromo-2-butyne in the presence of CuCl via a tandem inter-intra-molecular cyclization to yield 2,3,4,5-tetrasubstituted styrenes (Equation 11) <2002T1107>. 3-Chloro-(2-chloromethyl)propene reacts with the same set of zirconacyclopentadienes in the presence of CuCl to yield tetrasubstituted methylene cycloheptadienes. Reaction with 3,4-dichlorobutene under identical conditions yields vinylcyclohexadienes. In both cases, tandem inter-intra-molecular allylation occurs. 

Reaction of the 1,3-dithiolane derived from propiophenone with the reagent hexafluoro-propene-diethylamine and 1,3-dibromo-5.5-dimcthylhydantoin (DBH) yields the vinylic fluoride instead of the expected gem-difluoroalkane (see Section 1.1.7.2.). "... 

The anti addition of diethyl 7V,Ar-dibromophosphoramidates to acyclic and cyclic alkenes was achieved in the presence of boron trifluoride, which makes the ionic dissociation of the N —Br bond more labile94,9s. After reduction of the initial /J,lV-dibromo adducts with sodium bisulfite, the /i-bromo-A -hydrophosphoramides 3 precursor of / -bromo amine hydrochlorides 4 were obtained (Table 4). However, a mixture of diastereomers was obtained from (Z)-l-phenyl-l-propene and (E)- and (Z)-l,2-diphenylethylene. Direct assignment of stereochemistry by H NMR of the phosphoroamidates derived from 2-butenes was not possible. Detailed analysis is, however, possible for the H-NMR spectra of the /J-bromo amine hydrochlorides. As determined by 31P NMR spectroscopy all additions to unsymmetrical aliphatic alkenes were not regiospecific. The /f-bromo amine hydrochlorides were converted to 1,2-diamines95. 

Compound 4.8 is (7.v-dichlorobis(triethylphosphine)plat-inum(II) compound 4.9 is //Y///.y-tetramminebis(dimethylamido)-cobalt(IIl) ethoxide compound 4.10 is bis[c/ y-dibromo( i -dimethyl SLilfide)platinum(lI)] compound 4.11 is benzenethiolatochloro(ri--propene)palladium(Il). 

C2H8CINS b-mercaptoethylamine hydrochioride 156-57-0 25.00 1.0896 2 1507 C3H4Br2 trans-1,3-dibromo-1 -propene 32121-07-6 20.00 1.9791 1... 

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